The present invention relates generally to semiconductor manufacturing and, more specifically, to the conditioning of polishing pads used for chemical-mechanical polishing (CMP).
Chemical-Mechanical Polishing (CMP) is a key processing technology for fabricating semiconductor chips. Often, after the performance of a processing step, the resulting wafer surface is full of peaks and valleys. Peaks and valleys of subsequent processing steps can build upon one another, creating an uneven surface that may be undesirable for a number of reasons. CMP uses a polishing pad and a slurry of chemically active liquid and abrasive material to grind down the surface of a wafer, thus restoring the planar surface.
In particular, CMP is useful for planarizing intermetal dielectric layers of silicon dioxide or for removing portions of conductive layers within integrated circuit devices. Non-planar dielectric surfaces may interfere with the optical resolution of subsequent photolithography processing steps, making it extremely difficult to print high-resolution lines. The application of a second metal layer over an intermetal dielectric layer having large step heights can result in inadequate metal coverage, and ultimately in an open circuit.
FIG. 1 illustrates an exemplary linear CMP process. A semiconductor wafer 20 is typically held face down against a flat polishing pad 22 that has been coated with the slurry (not shown) and that moves relative to wafer 20 along arrow A. A rectangular conditioning pad 26 is used to condition polishing pad 22 continuously as wafer 20 is polished.
In an exemplary rotary CMP process, shown in FIG. 2, semiconductor wafer 20 is typically held face down and rotated along arrow C against a flat polishing pad 24 that has been coated with the slurry and that rotates along arrow B. Both wafer 20 and pad 24 are typically rotated relative to each other. Also shown in FIG. 2 are a first reference location 32 on polishing pad 24 and a second reference location 30 on polishing pad 24 located radially inward of location 32. As for the linear CMP process, rectangular conditioning pad 26 is used to condition polishing pad 24 continuously as wafer 20 is polished in the rotary CMP process. In both the linear and rotary CMP processes, the abrasive polishing process continues until the surface of wafer 20 contacting polishing pad 22 or 24 is substantially planar.
The motion of wafer 20 with respect to polishing pad 22, 24 and the force applied to hold wafer 20 against the pad adds mechanical energy to the system that helps remove the wafer surface material. In addition, the process of supplying fresh chemical liquid and removing spent chemical liquid helps remove material from the wafer surface. Uniform removal of material from the surface of wafer 20 is pursued by adjusting a number of variables, such as the pad velocity with respect to the wafer surface, the force applied between the pad and the wafer, and the slurry composition and flow.
Over time, the initially rough surface of polishing pad 22, 24 becomes worn and may glaze over due to a build-up of slurry and other deposits on the pad surface. To counteract the glazing and wear, polishing pad 22, 24 is periodically mechanically scored or xe2x80x9cconditioned.xe2x80x9d Conditioning pad 26 removes the build-up on polishing pad 22, 24 and roughens the surface of polishing pad 22, 24. Different approaches to conditioning may be required depending on the hardness of the pad surface and the particular slurry used for polishing. Further, conditioning may be performed by a conditioning apparatus in a discrete conditioning step or during wafer polishing depending on the specific conditioning process and apparatus used. FIGS. 1 and 2 both show rectangular conditioning pad 26 that may be used to condition polishing pad 22, 24 continuously as wafer 20 is polished.
The polishing pad-and-slurry combination may be envisioned as a piece of sandpaper in which the slurry acts as the sand and the polishing pad acts as the paper on which the sand is mounted. The slurry may have different particle sizes, with larger particles providing more grinding of the wafer surface than smaller particles, similar to the difference between larger and smaller grit sandpaper. The more slurry held against the wafer surface or greater particle size of the slurry, the more grinding that may occur. Grooves in polishing pad 22, 24 drain the slurry away from the surface of the pad. Slurry in the grooves is thus ineffective or less effective at grinding than slurry on the surface of the pad.
The shape and volume of the grooves per unit area of polishing pad 22, 24 therefore control to some degree the amount of polishing. For example, larger grooves not only take more slurry away from the surface, but also may completely or partially trap larger particles. Small grooves that are unable to trap large slurry particles leave the large particles in contact with wafer 20, providing more grinding than parts of polishing pad 22, 24 where the grooves are large enough to allow such particles to be trapped in the grooves. Intermediate size grooves may only partially trap the particles, leaving portions of the large particles protruding and providing less polishing than where only small grooves are present, but more so than where large grooves are present. The depth of the grooves may further control how much of the slurry is drained away, deeper grooves providing areas with less polishing capability than in shallower grooves.
Thus, the polishing rate and uniformity of the CMP process may be greatly affected by the characteristics of the polishing pad surface, which can make the slurry more or less effective. The ability to optimize the pad surface during conditioning is therefore highly desirable.
The present invention provides a chemical-mechanical polishing pad conditioner comprising a non-uniform conditioning surface having a plurality of conditioning elements and at least a first section and a second section. The first section has a first cutting volume per unit width that is greater than the second cutting volume per unit width of the second section. The first section may include at least one first conditioning element having a first projected width whereas the second section includes at least one second conditioning element having a second projected width that differs from the first projected width. The first section may also or instead have a first plurality of conditioning elements with a first density whereas the second section has a second plurality of conditioning elements with a second density that is different from the first density. The first section may also or instead have at least one conditioning element with a first cutting depth whereas the second section has at least one conditioning element with a second cutting depth different from the first depth.
The conditioner may be adapted for use in a linear or rotary CMP operation, and may be rectangular or may be a roller-type conditioner. In a rotary application, the non-uniform conditioning surface may be designed to compensate for a difference in relative velocity of the polishing pad at a radial-inward location as compared to a radial-outward location.
The conditioner may further comprise a third, transition section between the first section and the second section. The third section has a third cutting volume per unit width intermediate the first and second cutting volumes per unit width. The third section also has a gradual transition in cutting volume per unit width between the first and second cutting volumes per unit width.
The conditioner may be an element in a chemical-mechanical polishing tool comprising a polishing pad, the conditioner, and a mechanism for moving the polishing pad relative to the conditioner. The mechanism may further be adapted to move the polishing pad relative to the conditioner in a linear or rotary manner.
The conditioner may be used to perform a method for providing uniform conditioning of a chemical-mechanical polishing pad. The method first comprises the step of identifying at least a first region of the polishing pad that requires a different volume of material removed by the conditioner than a second region of the polishing pad. Then, the conditioner is provided with a non-uniform conditioning surface having a first section with a first cutting volume per unit width positioned to contact the first region of the polishing pad and a second section with a second cutting volume per unit width positioned to contact the second region of the polishing pad. The conditioner is then used to condition the polishing pad.
The invention also comprises a chemical-mechanical polishing pad that results from use of the conditioner of this invention. Such a pad comprises a non-uniform polishing surface having a plurality of grooves and at least a first region and a second region. The first region has a first groove volume per unit area that differs from a second groove volume per unit area of the second region.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention.